The supply of natural wood fibers is restricted and has been curtailed. It is estimated that 1991 federal timber harvest levels for the Northwest United States will be reduced to from about 20% to about 40% of the 1990 levels.
Disposal of ever-increasing quantities of waste paper, particularly in urban areas, is an important environmental problem. Scarcity of landfill areas, and air pollution consequent from incineration render the development of alternative disposal methods imperative.
Environmentally acceptable recycling technology is required to concomitantly alleviate the waste paper disposal problem and to ease the demand for natural wood products.
Particle board, medium density fiberboard, hardboard, and other composites based on wood are widely used. The technology for manufacturing these wood-based composites is well developed. Prior to this invention, however, a practical and environmentally acceptable method for preparing useful composites entirely from waste paper or paperboard had not been developed.
U.S. Pat. No. 4,111,730 recognizes some of the benefits from waste paper recycling. To provide a paperboard product, waste paper is reduced to flake, conditioned to a low moisture content, blended with a thermosetting urea or phenol-formaldehyde resin, pressed into a mat, and cured. These board products may have a moisture content of 10-12%, a density of 19-75 pounds per cubic foot, and may be from 0.25 to 1.50 inches in thickness. The phenol-formaldehyde resin content renders these board products environmentally undesirable.
A composite board made from 100% waste paper fiber and melamine isocyanate urea-formaldehyde resin is described in Deppe, "The Utilization of Wastepaper and Refuse Fiber Material for Particle Board and MDF" Proceedings of the Nineteenth Washington State University International Particle Board/Composite Materials Symposium (1985).
U.S. Pat. No. 3,718,536 describes a particle board composed of shreds of thermoplastic resin coated paper. A thermoplastic resin binder such as polyethylene or polypropylene is added to the plastic coated paper shreds to facilitate composite board manufacture.
Various composite boards have been formulated from wood particles or fibers with isocyanate binders. See, e.g., Polyurethanes Forest Products Technical Paper (1989) (published by ICI Polyurethanes Forest Products Group, Martha Grove Road, West Deptford, N.J. 08066. U.S. Pat. No. 4,311,554 describes an incombustible particle board comprising a mixture of wood chips, a mineral substance and a binder which may be an isocyanate adhesive.